Signal-translating system



mvENToR n. son P. cAsE '1 BY ATroRN Y Reimer! Apr.2o,1943

` UNITED. STATES, PATENT ori-ics 'Y 22,302. H i

. SIGNAL-rmsmmd SYSTEM Nelson Perry Case, Great Neck, Y., assigner to Haseltine Corporation, a corporation o! Delaoriginal No. 2,264,019, usted November 25, 1941, Y Serial No. 365,459, November 13, 1940. Application for reissue January 28, 1943, Serial No;

11 claims. `(ci. 25u-ao) The present invention relates to .signal-translating systems and, more particularly, to such systems having a controllable translating charsignal input to the detector is below the predetermined level necessary tor satisfactory reproduction, either because the received signal is near the prevailing noise level or because'the receiver is appreciably mistuned from a strong desired signal, in whichl latter case the reproduction of signals is also distorted by'such mistuning. The silencing of a frequency-modulated carriersignal receiverwhen the receiver Vis appreciably mistuned from a desired carrier signal isadditionally desirable to suppress the reproduction of y the spurious responses resulting from the frequency-responsive characteristic of the carrier- Sllnal channels provided in thel receiver. l Many of the prior art noise suppression systems heretofore used in amplitude-modulated carriersignal receivers are n ot adaptable for use in 1requency-modulated carrier-signal receivers. The former class oi receivers include means i'or de'- riving from a received carrier signal an automatic amplification control bias or equivalent,

which is generally used also to contrai the operation oi the noise suppression system it included in the receiver. The automatic ampliiication control bias developed in a frequency-modulated carrier-signal receiver; on the other hand, is not suitable to control a noise suppression system ci.

the prior art since it hasl a substantially constant amplitude over a broadjuning range on either side oi' a -desired'carrier signal. This constantamplitude-characteristic results from the broad pass-band characteristic o! the carrier-Sinai amplifiers necessarily used in frequency-modulated carrier-signal .receivers. Any' attempt to narrow the range over which the automatic amtained in proper alignment with the frequency detector of the receiver only lwith exceedingly great diinculty. i

It is an object of the present invention, therefore, to provide a new and improved signal-translating system having a controllable translation characteristic and one which avoids onev or more of the above-mentioned disadvantages and limitationsof the prior art systems. It is a further object of the invention to provide a signal-translating system wherein a signaltranslating characteristic of the system is controlled in accordance with variations of the mean frequency of a frequency-modulated carrier signal from a predetermined frequency.

It is an additional object of the invention to provide a signal-translating system wherein variations ol' a characteristic oi' a frequency-modulated carrier signal from a predetermined value control the operation of an oscillation generator, the output of which controls, in turn, a characteristic of the signal-translating system.

In accordance with the invention, a signal- Atranslating system comprises an input circuit adapted to have signals applied thereto, and a signal-translating channel coupled to the input circuit. The system includes means for deriving p liflcaticn control bias or equivalent is substantially constant has generally proven unsatisfactory since any such attempt must m predicated upon the integration ofthe energy of themodu.-

lated-carrier signal only at and in proximity to its mean frequency Vand it is well known that' limited constant-amplitude range of the auto-v matic amplification control bias can be maina nrst unidirectional potential the magnitude of which varies witha characteristic ot a signal' applied to the input circuit, and means for deriving a second unidirectional potential the magnitude and polarity oi' which vary with variations of the signal characteristic in opposite senses from a predetermined'value. The system additionally is provided with a source of oscillations. means redrawing and its scope will ,be pointed out in the appended claims.

Referring now to the drawing. Fig. 1 is a circuit diagram, partly schematic, of a complete i'rebodyin'g the invention: Fig. ais a graph comprisl AVing curves representing frequency-voltage relations occurring at certain pointsin the arrangement of Fig. l and is used as an aid inV explaining the operation or the latter; Fig. 3 is a circuit dia- -gramvrepresenting `a modified form o! the invention; and Fig. 4 is a graph comprising curves representing frequency-voltage relations occurring at certain points in the arrangement ot Fig. 3.r

Referring lnow morev particularly to Fig. l,

` 22,302 `there is represented schematically a complete I having its input circuit connected to an antennal system II, I2 and having its output circuit conn ected to an oscillator-modulator I3., Connected in Vcascade with the oscillator-modulator I3, in

v the order named, are an intermediate-frequency amplifier I4 of one or more stages, an amplitude limiter I5, a frequency-modulation detector and A. V. C. supply I6, an audio-frequency amplifier I1 of one or more stages, and a sound reproducer Il. Coupled to the A. V. C. supply and tothe output of the frequency-modulation detector` of unit I6 is an automatic control system I9, more fully described hereinafter, the output of which is coupled to a control electrode of one or more of the tubes of the audio-frequency amplifier I1. An automatic amplification control-or A. V. C. circuit is connected between the output of the A. V. C. supply of unit I6 and the control elecfrodes of one or more of the tubes of the radiofrequency amplifier III, the oscillator-modulator I3, and the intermediate-frequency amplifier I4, inconventional manner.

It will be understood that the various units i-I9, inclusive, just described may, with the exception of the unit I3 presently to be considered, be of a conventional construction and operation, the details of which are well known in moment the operation of the automatic control system l2. presently to be described, a desired through tube 2|.

frequency-modulated carrier signal is selected mediate-frequency carrier signal in the oscillatormodulator I3, amplified in the intermediate-fre-` quency amplifier I4, limited to a predetermined substantially constant amplitude by the limiter I5, and detected by the frequency-modulation de tector of unit I6. thereby to derive the audio-frequency modulation components. I'he audio-frequency components are, in turn. amplified in the audio-frequency amplifier I1 and are reproduced by the sound reproducer I3 in a conventional manner.

. The automatic amplification control or A. V. C. bias derived from the A. V. C. supply of unit It is effective to control the amplification of one or more of the units I0, I3, and I4 to maintain the signal input to the limiter I5 within a relatively narrow range for a wide range of receivedsignal intensities.

Referring now more particularly to the portion of thefsystem embodying the present invention,- the audio-frequency amplifier I 1 comprises a signal-translating channel and it is desirable that a characteristic oi' .the channel be controlled in accordance with a characteristic of the carrier signal applied from the limiter Il to the input clr cuit of unit I3. Morevspeciflcally, it is desired that the amplification of the audio-frequency amplifier I1 be controlled in accordance with either or both the intensity of a received carrier signal and the diiIerence between the mean quency oi the frequency-'modulated intemistilatoDV frequency. carrier signal and that of bandupass selectors of the receiver, the control being such that the Areceivlyarf is silenced when the received carrier-"signal intensity is 4 frequency difierence'has a value corresponding to a predetermined mistuning of the receiver from a desired 'carrier signal. To this end, the A. V. C. supply of unit I6 comprises means for deriving a unidirectional potential the magnitude of which varies with a characteristic of the frequencymodulated intermediate-frequency carrier signal applied -to the input circuit of unit I6. The frequency-modulation detector of unit I3 comprises .means for deriving a second unidirectional potential, the magnitude and polarity of which vary with variations of the frequency of the intermediate-frequency signal carrier on either side of the mean frequency of the selector circuits. In this connection, it will be appreciated that the frequencyof the intermediate-frequency signal deviates over a predetermined range centered about its mean or nominal frequency.

The-automatic amplification control system I3 includes a source of oscillations "comprising an oscillation generator 2li which may be of any well-known type, but is shown as a. single tube multivibrator of the type disclosed in United States Letters Patent No. 2,203,519, granted June 4, 1940 to Madison Cawein. Briefly, the generator 2li comprises a vacuum tube 2I of the pentode Y type having its screen and suppressor directly is connected between the anode and ground, the

condenser being periodically and alternately charged through the anode load resistor 25 from the space current source +B and discharged included in the cathode lead while the control grid of Ytube 2| is coupled through a resistor 23 to the A. V. C. supply of unit I6. is coupled through a filter circuit comprising a series resistor 23 and a shunt condenser 30 to the output of the frequency detector of unit I3. and, lastly, is coupled through a resistor 3| tothe anode of a direct current amplifier tube 32. A negative-bias potential is developed across the suppressor grid-leak resistor 23 when the tube 2| is generating oscillations and this potential is applied through a filter network comprising a series resistor 33 and a shunt condenser 35 and through a resistor 34 to an amplification control circuit of the audio-frequency amplifier I1. In practice, the amplification control circuit of unit I1 generally comprises the control-grid circuit of the first amplifier stage of vunit I1.

The input circuit of the direct current am- 'plifler 32 is coupled through an audio-frequency .cuit of amplifier 32 includes a load resistor 33 Y drop across resistor 33 by grid rectification and 'too low orlthe aforesaid ifV consequently are not reproduced in the output of amplifier 32. Negative values of the detector output potential are amplified, however, thereby to derive in the output of amplifier 32 a unidirectional potentlal having positive polarity.

Thus, amplifier. 32 comprises means responsive.

A cathode-bias resistor 21 is cycles.

' .cuit elements n, vze, an, al,

ramplifier l! comprises means for vderiving a 1mi- .directional'potentiaL the magnitude of which varies with variations in one sense of the frequency of the signal carrier Vfrom a predetermined value, the polarity of this potential and the sense of variation thereof being opposite to that. of the detector output potential with variation in the one sense of the signal-carrier frequency from the aforesaid predetermined value.

In considering the operation of the circuit just described, reference may be had to the aforementioned-Patent 2,203,519 for a description of the detailed operation of the oscillation generator 20, per se. Briefly, however, for purposes of vthe present description of the system operation,

which potential isapplied through condenser 22 to developacrcss the suppressor grid resistor Il an alternating potential having small positive half-cycles and relatively large negative half-- This particular type of generator possesses the important characteristic that the amplitude of the output saw-tooth oscillations developed, and the grid bias developed across grid resistor 23 by grid rectification, are, forpurposes of the' present invention,l substantially independent of variations of bias applied to the input electrodes of the generator.

\ The generator 20 possesses the additional important characteristic Athat the generation of oscillations is suddenly terminated whenV the negative biasing potential applied to the control grid of tube 2i exceeds a predetermined magnitude and'the generator remains inactive until' such negative bias is reduced to a value lower than that at which the generator ceased to oscillate. Thus, this type of generator'has, more or lless inherently, the property of either oscillating tor 2l is controlled only by the effective time constant of its input circuit, comprising the cir- 3l, I1, Il and the circuit elements included in the output circuits of the A. V. C. supply and the frequency detector of unit it, and by the timec onstant of its output circuit,`comprising the circuit elements 23, 3l, ll, 3l and the circuit elements included in the control circuitof unit i1. 'I'hese time the lack of a transition region.

Assuming that the intensity of a received carrler signal is constant, the curves of Fig. 2 show the magnitudes of the unidirectional potentials developed by the frequency detectorand by the A. V. C. supply of unit it, that developed in the l 'output circuit of amplifier 32, andthe approximate resultant control bias applied to the grid of oscillation generator 2li with variations of frequency of the intermediate-frequency carrier signal, the value of the approximate resultant control bias being arrived at under the assumption that no` grid current'is drawn by generator 2l when the grid is biased positively. Curve A represents the unidirectional4 potential derived by the A. V. C. supply of unit IB, the magnitude of this potential usually being substantially constant, as indicated, over the range of frequency deviation of the intermediate-frequency carrier signal. Curve B represents the unidirectionalv potential derived from the intermediatefrequency Vcarrier signal by the frequency detector of unit il which, it is seen, varies linearly but in opposite senses, on either side of the meanresonant frequency fn of the selector circuit of unit I6. This latter potential is applied to the input circuit of amplifier I2 and there is derived at the anode thereof a unidirectional potential represented by curve C. From curve C it will be seen that the potential oi the anode of amplifier. is at all'times positive, but;has a low substantlally constant value during thetime that the output potential of the frequency detector il is positive, due to the large potential drop developed across resistor ll by grid current lof the amplifier 32, and that the anode potential increases linearly with frequency for increasingly negative values of detector output potential. Since the outputs of the A. V. C. supply and the frequency detector of unit I6 and the output of amplifier 32 are allapplied to the control grid ofgenerator 20. the'resultant potential applied to the control grid is a resultant voltage,V thevalues of which are generally represented*l by curve D of Fig. 2. It will be seen from the resultant curve D that the control gridof genera- 'tor 20 is negativeas long as the .frequency of The oscillation generator 2li suddenly breaks into'oscillation when a small positive potential, represented in Fig. 2 by the potential e, is applied to its control grid and suddenly ceases oscillating when its control grid is negatively biased. From this, it is evident that no bias is developed across the suppressor grid resistor 23, and Ath'eaucliofrequency' amplifier i1 consequently has normal ampliflcations, during the time when the mean frequency of the intermediate-frequency carrier signal lies substantially within the frequency range I to -'f. It may here be noted that, while nal deviates over a range wider than the limited range l to .-f by virtue of its frequency modula- Y- tion, so that it might appear that the resultant tensity, or critical value of frequency of the intermediate-frequency carrier signal.. it .is ap-` parent that the control system i9. is free from such distortion. Obviously, there also can be no undesirable volume control effect when the automatic control biss -applied to unit i1 is either normal or far beyond cutoff. This further ad carrier lies outsidev of the frequency range f to -f.

the grid of generator 2l is biased positively, it

oscillates in a normal manner,V a large negative the frequency of the intermediate-frequency sigbias is developed across the suppressor grid resistor 23, and the audio-frequency amplifier il is biased beyond cutoff, thereby silencing the receiver. I

The receiver is similarly silenced in the event that a desired received carrier signal does not have sumcient intensity to ensure satisfactory reproduction, the operation being substantially the same as in the foregoing described operation except that the slope of the detector output characteristic, represented by curve B of Fig. 2, is not as greatvfor carrier signals of low intensity and the magnitude of the A. V. C. bias, represented by curve A of Fig. 2, is correspondingly smaller. Thus it will be evident that 'generator 20 continues to oscillate, thereby silencing the receiver, until such time as the received carrier signal is accurately tuned in and has a sufficiently large intensity that the negative bias derived by the A. V. C. supply of unit I'B is larger in magnitude than the positive bias applied to the control grid of tube 2| from amplifier 32.

From the foregoing description of the operation of the invention, it will be seen that the lcontrol grid of generator 20 and its associated control circuit comprise means responsive to the unidirectional potentials derived by the A. V. C. supply and frequency detector of unit l5 for modifying theV amplitude characteristic of the oscillations of generator 2li. The control circuit of unit Il is responsive vto such amplitude characteristic of the generated oscillations for controlling the amplifying characteristic of the audio-frequency amplifier l1. It will furtherbe seen that the detector andA. V. C. supply of unit I6 and the amplifier 32 together constitute means responsive to the frequency characteristic of the intermediate-frequency signal carrier for deriving a unidirectional potential having a negative polarity when the frequency characteristic of the signal carrier has apredetermined range of values and having a positive polarity .when the value of the carrier frequency is above or below the predetermined range of values.

It ls evident from curve D of Fig. 2 that the bias applied to the control grid of generator 20 may vbecome negative, thereby to allow the audiofrequency amplifier il'to operate with full output, in the event that. the receiver is so badly mistuned from the desired carrier signal that the mean frequency of the intermediate-frequency signal carrier departs farther than a frequency f1 from the desired intermediate frequency. This. of course. is a condition of loperation which in certain cases may be `undesirable and which arises from the fact that the potential of the anode of amplifier 32 increases only to a predetermined value of potential; thereafter, increasingly larger negative values of detector output eventually bias the .grid of generator 20 negatively, as indicated by curve D. Such an operating condition is avoided by the arrangement of Fig. 3 which is a circuit diagram representing a modified form of the automatic control system essentially similar to the corresponding system I9 of Fig. 1, similar circuit elements being designated by similar reference characters. In this'embodiment the negative values of unidirectional potential developed in the output of the detector of unit I8l are prevented from lreaching the control grid of generatory2ll by the insertion of a unilaterally conductive or rectifier device 39 in the coupling circuit between the output of the `detector of .unit IBy and the control grid of generator 20.

Thus, the rectier device 38 comprises means for deriving from the detector output potential a unidirectional potential having zero value when the frequency ofthe signal carrier is below a predetermined value and having a given polarity when the signal-carrier frequency is above this predetermined value. The arrangement of Fig. 2 also includes a tuning indicator device, which may be of the 6E5 type of vacuum tube, the control grid of which is coupled through a resistor 4I to the control grid oi" tube 2|. The tuning indicator device Ill is energized from a source of space current-H3.

The operation of this modified form of the inven'tlon is essentially similar to that of the Fig. 1 arrangement except that only positive values of unidirectional potential are applied from the detector of unit lBvto the control grid of generator 2i!V by virtue of the unilaterally conductive properties ofthe device 35. Assuming that the intensity of a received carrier signal is constant, the curves of Fig. 4 show the several unidirectional voltages and the resultant unidirectional voltage applied to the control grid of generator 20, the value of the resultant voltage being arrived at under the assumption, as before, that the grid of generator 2li does not draw glid current when positively biasd. Curve A1 represents the unidirectional potential applied to the control grid irom the A. V. C. supply of unit Ii. Curve B1 represents the unidirectional potential applied to the control grid from the detector of unit I6. there being only positive values of this voltage by virtue of the device 38. Curve Ci represents the unidirectional voltage applied to the control grid from the output of amplifier I2. The magnitude of the resultant of these several voltages is represented, in general, by curve D1 from which it is evident that the control grid of generator 20 can become negative only when the intermediate-frequency signal carrier has a mean frequency lying within the limited frequency range f to J. Consequently, the receiver is silenced at all times except when the intermediate-frequency signal carrier has a frequency very close to that of the desired intermediate frequency. Thus, amplifier 32 and the yrectifier device 3'9 comprise means for deriving fromrthe unidirectional voltage of the detector of unitV I6 a second unidirectional voltage the magnitude of which varies positively from a predetermined value with variations of the i'requency of the intermediate-frequency signal carrier in opposite senses from the predetermined desired intermediate frequency.

The bias. applied to the control grid of tube 2l is also applied to the grid of the tuning indicator` device lllv thereby to change the shadow angle of this device in accordance with the tuning oi'l Athe receiver to a desired carrier signal, the

shadow angle being a minimum when the receiver accurately ls tuned to the desired carrier signal.

Thus, the condition 'of tuning of the receiver to` channels. Thus, in the arrangement of Fig. 3, when the receiver is appreciably detuned from a carrier signal, the output ofy both the detector and A. V. C. 4supply of unit I6 is zero and the only bias applied to the control grid of vacuum tube 2| is a small constant positive bias derived from the output ofthe amplifier 32. This positive bias, of course, causes the generator 2p to generate oscillations, thereby to produce a neg tive bias across the resistor 23 which blocks e audio-frequency amplifier l1 to silence the output of the receiver. This described operation applies also to the Fig. 1 arrangement except for ,a small range of carrier-signal frequencies in the vicinity of the frequency f1. Fig. 2, where, as explained above, the generator 20 may cease to generate oscillations due to the negative values of curve D for such frequencies. l

While in the arrangements of Figs. 1 and 3 the negative bias applied through the resistor 2l to the control grid of tube 2| is derived from the A. V. C. supply of unit l0, this bias may alternatively be derived from a source of constant potential, as, for example, a battery. However, where the bias isderived from a source of constant potential, the bias applied to the control grid of tube 2l is negative and has the same value either when the receiver is accurately tuned to a -desired carrier signal or when the receiver is not tuned, to yany carrier signal as when tuned between carrier-signal transmission channels. In certain cases, this type of operation may be undesirable since the resultant negative bias apr plied to the control grid of tube 2| causes the generator 20 to cease generating oscillations, whereby the audio-frequency amplier I1 has normal amplification, whenever the receiver is not tuned to proximitv with a carrier signal. Thus lnterchannel noise is received when tuning between stations, a condition of operation which is avoided by the arrangements of Figs. l and 3. l As illustrative of a specinc embodiment of the invention, the following -circuit constants are given for an embodiment of the invention shown in Fig. 1:

sacos' While there have been described what are at present considered to bethe preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modications maybe made therein without departing from-the invention, and it is, therefore, aimed y in the appended claims to cover all such changes Vacuum tube 2| i --r --Type GSJ'I Vacuum tube 32 Type SSFS Resistor 23 megohm.... 1 Resistor 24 --ohms.. 68,000 Resistor z s dn 50,000 Resistor 21 do 220 Resistor 2.8.. ....do 670,000 Resistor 29 megohms 1 l Resistor ll -..do- 15 Resistor 33 dn 3 Resistor dn 10 Resistor IB do 1 Resistor 38 dn 15 Condenser 22.... ....micro-microiarads 3,000 Condenser 20 ..-do 2,000 Condenser 30 microfarad 0.02 Condenser 3l --do 0.01 Condenser Il.. -d 0.02 +B volts-- 250 Mean intermediate frequency` megacycles-.. 4.3

` arrangement except as follows:

Resistor 28 .megohms- 3.3 Condenser 30 .microfaradn 0.01

Device 39-------....----- Type 6K6 vacuum tube 7g and modifications as fall within the truespirit and scope of the invention.

What is claimed is:

l. A signal-translating system comprising, an input circuit adapted to have signals applied thereto, a signal-translating channel coupled to said input circuit, means ior deriving a first unidirectional potential the magnitude and polarity of which vary with variations of a characteristic of an applied signal in opposite senses from a predetermined value, means for deriving a second unidirectional potential the magnitude of which varies with variations in one sense oi said characteristic from saidpredetermined value, the 'polarity of said last-named potential and the sense of variation thereof being opposite to that of said'iirst-named potential with variations in said one sense of said characteristic from said predetermined value, and means responsive jointly to said derived unidirectional potentials for controlling a characteristicof said signaltranslating channel.

2.' A signal-translating system comprising. an input circuit adapted to have signals applied thereto, a; signal-translating channel coupled to controlling a characteristic of said signal-translating channel.

3. A signal-translating channel comprising, an t -input circuit adapted to have signals applied thereto, a signal-translating channel coupled to said input circuit, means responsive to a characteristic of an applied signal for deriving a unidirectional control potential having one polarity when said characteristic has a predetermined value and having opposite polarity when the value of said characteristic differs above or below said value by a predetermined amount, a source of oscillations, means responsive to said derived unidirectional potential for modifying a characteristic of the oscillations of said source,

\, and means responsive to said characteristic of said oscillations for controlling a characteristic of said'signal-translating channel.

4. A signal-translating system comprising, an input circuit adapted to have signals applied thereto, a signal-translating channel coupled to r said input circuit,- means for deriving a irst unidirectional potential the magnitude and polarity of which 'vary with variations of a characteristic of an applied'signal in opposite senses from a predetermined value, means for deriving a second unidirectional potential the magnitude of which varies with variations in one sense of said characteristic from a predetermined value, the polarity of said last-named potential and the' sense of the variations of magnitude thereof being opposite to that of said nrst unidirectional potential with variations in said one sense of said characteristic ,from said predetermined value, a source of oscillations, means responsive `jointly to said derived unidirectional potentials for modifying a characteristic of the oscillations of said source, and means responsive to said characteristic of said oscillations for controlling a characteristlc of said signal-translating channel.

5. A 'signal-translating system comprising, an

`input circuit adapted to have signals applied thereto, a signal-translating channel coupled to said input circuit, means responsive to a chari- .acteristic of 'an applied signal for deriving a uni directional potential having one polarity when said characteristic is below a predetermined value and having opposite polarity when said characteristic is vabove said predetermined v'alue,

means for deriving from said unidirectional poy tential of said one polarity a second unidirectional potential having said opposite polarity, a source of oscillations,v means responsive jointly to said unidirectional potentials of said opposite polarity for modifying a characteristic of the oscillations of said source, and meansresponsive to said characteristic of said oscillations for controlling a characteristic lof said signal-translating channel.

j 6. A signal-translating system comprising, an inputvcircuit adapted to have signals applied thereto, a signal-translating channel coupled to said input cirbuit, means responsive to a. charpolarity, a source of oscillations, means responsive jointly to said unidirectional potentials of said opposite polarity for modifying a characteristie of the oscillations of said source, and means responsive to said 'characteristic of said oscillat tions for controlling a. characteristic vof said signal-translating channel.

7. A signal-translating system comprising, an input circuit adapted tohave carrier signals applied thereto, a signal-translating channel coupled to said input circuit, a frequency detector coupled to said input circuit for deriving from an applied signal a unidirectional potential having one polarity when the frequency of said carrier signal is below a predetermined frequency and having opposite polarity when the value of said carrier-signal frequency is above a predetermined frequency, an audio-frequency nlter network, a direct current amplifier coupled through said network to said frequency detector for deriving from said unidirectional potential of said one polarity a second unidirectional potential having said opposite polarity, a source of oscillations, means responsive jointly to said derived unidirectional potentials of said oppositepolarltles for modifying a characteristic of the oscillations of said source, and means responsive to said char- Y acteristic of said oscillations for controlling a characteristic of said signal-translating channel.

8. A signal-transliaitinii system comprising, an input circuit adapted to have signals applied thereto, a signalwampliencoupled to said input circuit. incolla for'dcrivinla nrst unidirectional acteristicof an applied signal for deriving a' potential the magnitude and polarity of which vary with variations of a characteristic of an applied signal in opposite senses from a predeteri mined value, means for deriving asecond unidirectional potential the magnitude of which varies with variations in one sense of said characteristic from said predetermined value, the polarity of said second unidirectional potential and the sense of variation of the magnitude vthereof being opposite to that of said nrst unidirectional potential with .variations in said one sense of said characteristic from said predetermined value, a source of oscillations, means'responsive jointly to said de- -rived unidirectional potentials vfor modifying a.

characteristic of the oscillations of said source, and means responsive to said characteristic of said oscillations for controlling the amplication of said signal amplier.' i

9.- A signal-translating system comprising, an input circuit adapted to have signals appliedthereto, a signal-translating channel coupled to said input circuit, means responsive to a characteristic of an applied signal for deriving a first unidirectional potential having one polarity when said characteristic is below a predetermined value and having opposite polarity when said characteristic is above said predetermined value, means for deriving from said nrst unidirectional potential of said one polarity a second unidirectional potential having said opposite polarity, means for deriving from said nrst `unidirectional potential a third unidirectional potential having zero value when said characteristic is below said predetermined value and having said opposite polarity when said characteristic is aboveisaid predetermined value, a source oi' oscillations, means responsive jointly to said second and third unidirectional potentials for modilylng a characteristic of the oscillations of said source, and means responsive to said characteristic of saidl oscillations for controlling a characteristic of said signal-translating channel. q

10. A signal-translating system comprising, an input circuit adapted to have signals applied thereto, a signal-translating channel coupled to said input circuit,rmeans responsive to a characteristic of an applied signal for deriving a first unidirectional potential having one polarity when said characteristic is below a predetermined value and having opposite polarity when said characteristic is above said predetermined value, means for deriving from said :first unidirectional potential of said one polarity a second unidirectional potential having said opposite polarity, means including a unilaterally conductive device for deriving from, said'nrst unidirectional potential a third unidirectional potentialV having zero value when.l said characteristic is below said predetermined value and having said opposite polarity `when said characteristic is above said predetermined value, a source of oscillations,A means responsive, jointly to said second and third unidirectional potentials for modifying a'characteristic of the oscillations of said source, and nieans responsive to said characteristic or said oscillations vfor controlling a characteristic oi' saidvsignaltranslating channel. a

11. A signal-translating system comprising, an input circuit adapted to have signals .applied thereto, a signal-translating channel coupled to ,n

. said input circuit, means for deriving a first unidirectional potential the magnitude of which varieswith a characteristic of an applied signal, means responsive to a characteristic of said applied signal for deriving asecond unidirectional potential having one polarity when said' lastnamed characteristic is below a predetermined Value and having opposite polarity when said last-named characteristic is abovesaid predetermined value, means for deriving from saidl second unidirectional potential of said one polarity a third unidirectional potential having said opposite polarity, a source of oscillations, means responsive jointly to said rst, second. and third unidirectional potentials for modifying a chary acteristic of the oscillations of said source. and means responsive to said characteristic of said `oscillations for controlling a characteristic of said signal-translating channel.

NmsoN PERRY CASE. 

